microsoft ado net entity framework step by step

Contents at a glanceIntroduction xvii PART I INTRODUCING THE ENTITY FRAMEWORK ChAPTEr 1 Getting to know the Entity Framework 3 ChAPTEr 2 Looking more closely at queries 29 PART II COMP

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Microsoft ADO.NET Entity Framework Step by Step

John Paul Mueller

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This book is dedicated to Kevin Smith, a good friend who’s helped us realize some of our most special dreams He’s always helped us help ourselves—an outstanding gift that’s exceptionally rare in this world.

—John Paul Mueller

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Contents at a glance

Introduction xvii

PART I INTRODUCING THE ENTITY FRAMEWORK

ChAPTEr 1 Getting to know the Entity Framework 3 ChAPTEr 2 Looking more closely at queries 29

PART II COMPLETING BASIC TASKS

PART III MANIPULATING DATA USING THE ENTITY FRAMEWORK

ChAPTEr 7 Manipulating data using entity SQL 147 ChAPTEr 8 Interaction with stored procedures 175

ChAPTEr 10 Interaction with Table-Valued Functions 213 PART IV OVERCOMING ENTITY ERRORS

ChAPTEr 12 Overcoming concurrency issues 265 ChAPTEr 13 handling performance problems 287 PART V ADVANCED MANAGEMENT TECHNIQUES

ChAPTEr 15 Mapping data types to properties 347 ChAPTEr 16 Performing advanced management tasks 369

Index 405

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Introduction xvii

PART I INTRODUCING THE ENTITY FRAMEWORK Chapter 1 Getting to know the Entity Framework 3 Defining an entity 4

Understanding the Entity Framework elements 6

Considering the conceptual model 7

Considering the storage model 8

Considering the model mappings 8

Introducing the Entity Framework files 9

Viewing the Conceptual Schema Definition Language file 9

Viewing the Store Schema Definition Language file 11

Viewing the Mapping Specification Language file .11

Developing a simple Entity Framework example .12

Starting the Entity Data Model Wizard 12

Using the Entity Data Model Designer 16

Working with the mapping details 18

Using the resulting framework to display data 22

Getting started with the Entity Framework 26

Chapter 1 quick reference 27

Chapter 2 Looking more closely at queries 29 Defining a basic query 30

Creating the model 30

Working with enumerations 31

Obtaining an application data source 33

Creating the test application 36

Running the basic query 39

Creating specific queries 41

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Using operators, properties, and methods 42

Combining and summarizing data .44

Grouping data 45

Chapter 3 Choosing a workflow 49 Understanding the code-first workflow 51

Understanding the model-first workflow 53

Understanding the database-first workflow 54

Defining the workflow choices 55

Creating a code-first example .57

Creating a project .57

Defining the initial classes .58

Adding Entity Framework 5 support .59

Creating a code-first context 60

Adding a record .61

Viewing the results 63

Creating a model-first example 66

Defining the database model .66

Adding a record and viewing the results 70

Creating a database-first example 71

Reverse engineering the database model 71

Adding a record and comparing results .73

PART II COMPLETING BASIC TASKS Chapter 4 Generating and using objects 79 Understanding the Entity objects .80

Considering object services 80

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Working with an EntityCollection 82

Understanding the role of Entity SQL .84

Making queries using objects 85

Considering the role of lambda expressions 86

Creating a basic query using Entity SQL .86

Creating a basic query using LINQ 88

Modifying data using objects 89

Adding the forms 90

Adding purchases 92

Updating purchases 93

Deleting purchases .95

Working with Query Builder methods .97

Chapter 5 Performing essential tasks 101 Defining the essential tasks 101

Viewing the data 102

Saving changes 104

Inserting new values 104

Deleting old values .105

Creating a master/detail form 106

Creating the data source .106

Configuring the data source .109

Adding and configuring the controls 110

Testing the result 112

PART III MANIPULATING DATA USING THE ENTITY FRAMEWORK Chapter 6 Manipulating data using LINQ 119 Introducing LINQ to Entities 120

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Developing LINQ to Entities queries 122

Defining the LINQ to Entities essential keywords 125

Defining the LINQ to Entities operators 127

Understanding LINQ compilation 135

Following an IQueryable sequence 135

Following a List sequence 138

Using entity and database functions 139

Creating the function .139

Accessing the function 142

Chapter 7 Manipulating data using Entity SQL 147 Understanding Entity SQL 148

Considering the Entity SQL data flow 148

Defining the Entity SQL components 149

Selecting data 159

Working with literals in Entity SQL 161

Using the standard literals 161

Adding some additional data .162

Using a date or time literal 164

Interacting with a decimal literal 166

Ordering data 168

Grouping data 169

Chapter 8 Interaction with stored procedures 175 Understanding stored procedures 176

Adding stored procedures to your model 179

Defining the stored procedure using Server Explorer 179

Testing the stored procedure 181

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Modifying a stored procedure 184

Building an application using stored procedures 188

Creating a basic stored procedure example .188

Chapter 9 Interaction with views 193 Understanding views 194

Adding views to your model 196

Defining views using Server Explorer 196

Testing the view 198

Updating the model .200

Creating a basic view example 202

Making views writable 204

Chapter 10 Interaction with Table-Valued Functions 213 Understanding TVFs 214

Comparing TVFs to views 214

Comparing TVFs to stored procedures .215

Defining the storage layer 215

Defining the mapping layer 216

Defining the conceptual layer 217

Defining the object layer .218

Adding TVFs to your model 218

Defining the TVF using Server Explorer 219

Testing the TVF 221

Updating the model .223

Calling a TVF using Entity SQL 225

Calling a TVF using LINQ 227

Mapping a TVF to an entity type collection .228

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PART IV OVERCOMING ENTITY ERRORS Chapter 11 Dealing with exceptions 237 Understanding exceptions .238

Considering exception sources 240

Dealing with the System.Data.EntityException 240

Working through System.Data namespace exceptions 242

Working through System.Data.Common namespace exceptions 246

Working through System.Data.Linq namespace exceptions .247

Handling connection string exceptions .248

Seeing the connection string problem 248

Creating code for the connection string problem 250

Adding another layer of exception handling .253

Dealing with query exceptions 256

Dealing with other data exception types 258

Understanding concurrency exceptions 261

Chapter 12 Overcoming concurrency issues 265 Visualizing database concurrency issues .266

Considering optimistic concurrency problems 268

Rejecting the change 269

Performing a partial update 270

Obtaining user input 270

Ignoring concurrency issues completely 270

Performing a forced update 271

Implementing optimistic concurrency in an application 271

Developing the test environment 272

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Testing the default concurrency 275

Coding for field changes 277

Using field-specific concurrency 279

Using row-version concurrency 282

Considering pessimistic concurrency issues 284

Chapter 13 Handling performance problems 287 Understanding performance issue sources 288

Considering the layers 288

Retrieving too many records 289

Using the local cache 290

Relying on pregenerated views 290

Relying on precompiled queries 293

Disabling change tracking 294

Choosing between lazy loading and eager loading 294

Viewing performance issues 295

Direct query viewing 295

Using third-party products .301

Defining the performance triangle 302

Considering the effects of raw speed 303

Considering the effects of security 305

Considering how raw speed and security affect reliability 309

Using multithreading as an aid to speed 312

PART V ADVANCED MANAGEMENT TECHNIQUES Chapter 14 Creating custom entities 319 Developing POCO classes 320

Configuring the model 320

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Adding the classes 322

Creating an ObjectContext class to interact with the POCO classes 325

Testing the POCO application 326

Creating a DbContext class to interact with the POCO classes 328

Creating the classes in a different project 330

Creating and using event handlers 337

Handling ObjectContext events 337

Creating and handling custom events 339

Creating custom methods 341

Creating custom properties .343

Chapter 15 Mapping data types to properties 347 Understanding mapping automation configuration 348

Configuring properties 349

Changing property mapping 351

Filtering the data 352

Working with standard data types .354

Considering the standard data type mapping scenarios 354

Creating the Rewards3 database 355

Performing standard data type mapping 358

Working with enumerated data types .361

Working with complex data types 363

Working with geography and geometry spatial data types 366

Chapter 16 Performing advanced management tasks 369 Developing multiple diagrams for a model 370

Creating the new diagram 371

Configuring the diagram appearance .374

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Performing batch imports of stored procedures and functions 376

Mapping a stored procedure that returns multiple result sets 377

Creating the stored procedure .378

Using the code-access technique 380

Using the EDMX modification technique 383

Creating entities with inheritance 387

Creating the Rewards4 database 387

Using inheritance with the model-first workflow 388

Using inheritance with the code-first workflow 394

Controlling context actions for automatically generated classes 400

Index 405

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Gaining access to data in a managed way without a lot of coding—that’s a tall order!

The Entity Framework fulfills this promise and far more Each version of the Entity

Framework is more capable than the last The latest version, Entity Framework version 5,

provides you with access to far more database features with less work than ever before,

and Microsoft ADO.NET Entity Framework Step by Step is your gateway to finding just

how to use these phenomenal new features In this book, you get hands-on practice

with all the latest functionality that the Entity Framework provides By the time you

finish, you’ll be ready to tackle some of the most difficult database management tasks

without the heavy-duty coding that past efforts required

Fortunately, this book doesn’t get so immersed in high-end features that it forgets

to tell you how to get started Unlike a lot of tomes on the topic, this book starts simply

and helps you gain a good foothold in understanding just why the Entity Framework

is such an amazing addition to the your developer toolbox You’ll see examples where

the automation does just about everything for you with little coding required, and

yet you obtain professional-looking results In fact, that’s what you’re buying with the

Entity Framework—a reliable means of creating code quickly and successfully without

the problems that would ensue if you tried to create the same code completely by

hand The book’s 44 examples help you gain experience using the Entity Framework in

a hands-on environment where you actually create code, rather than just reading about

what might work

Of course, you do eventually delve into higher-end topics You’ll find an entire

chapter on one of the most requested features, Table-Valued Functions (TVFs) Access

to this feature alone makes the upgrade to Entity Framework 5 a significant one You’ll

also discover how to handle performance problems and perform low-end tasks such as

using inheritance when creating a model In short, by the time you finish this book, you

will have the experience required to handle every common task that developers need

to know how to perform

Who should read this book

Anyone who creates database applications using ADO.NET and is tired of writing reams

of code will definitely benefit from reading this book What you should ask yourself is

whether you want to become more productive while writing code that is both more

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reliable and better able to interact with the database Although the coding examples are written in C#, several Microsoft Visual Basic developers tested this book during the writing process and found that they could follow the examples quite well All you really need is a desire to write database applications more quickly and with less fuss.

Assumptions

To use this book successfully, you need a good knowledge of database programming concepts using a technology such as ADO.NET Although every attempt is made to ex-plain basic (and essential) topics, a knowledge of working with databases using the NET Framework will make working through the examples significantly easier

You also need to know how to write applications using the C# programming guage All of the examples are written using C#, and there isn’t any attempt to explain how the language elements work If you don’t have the required C# knowledge, you

lan-should consider getting John Sharp’s Microsoft Visual C# 2010 Step by Step (Microsoft

Press, 2010)

Some of the examples also require some knowledge of Transact-Structured Query Language (T-SQL) Again, there are plenty of comments provided with the various scripts, but there isn’t a lot of additional information provided about language ele-ments The book assumes that you know how basic SQL queries work

Who should not read this book

This book is most definitely not aimed at the complete novice You must know a little about both SQL and ADO.NET to work with the book successfully In addition, you must know the C# programming language fairly well The examples in the book focus a little more on enterprise developers, but hobbyists should be able to follow the examples without problem If you’re looking for a high-end book with lots of low-end program-ming examples and no hands-on techniques, this is most definitely not the book for you This book is all about getting people started using the Entity Framework in a meaningful way to perform most common tasks, which means it uses several different techniques to convey information so that a majority of readers can understand and use the material presented

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Organization of this book

This book is organized into five parts Each part is designed to demonstrate a

particu-lar facet of the Entity Framework, with an emphasis on the functionality provided by

version 5 Here is a brief overview of the book parts (each part introduction has more

detailed information about the content of the chapters in that part):

■

■ Part I: Introducing the Entity Framework This part of the book introduces

you to the Entity Framework version 5 You’ll discover what is new in this version

of the Entity Framework and also basic concepts such as the parts of a model

Unlike many other texts, this part also tells you about the three workflows

avail-able when working with the Entity Framework: model first, database first, and

code first Every chapter includes coding examples that emphasize the basics so

that you can see precisely how the Entity Framework works at a basic level

■

■ Part II: Completing basic tasks Once you have a basic understanding of

what the Entity Framework does and why you’d want to use it, it’s time to see

how to perform basic Create, Review, Update, and Delete (CRUD) operations

This part of the book provides an essential discussion of how to perform

es-sential tasks with full automation in place It’s the part of the book you want to

read to emphasize speed of development over flexibility in accessing database

functionality

■

■ Part III: Manipulating data using the Entity Framework Most applications

require more than a display of raw database data and simple CRUD operations

This part of the book takes the next step in your journey of actually controlling

how the data appears and precisely what data is retrieved from the database

You discover two client-side techniques for manipulating data (Language

Integrated Query [LINQ] and Entity Structured Query Language [Entity SQL])

In addition, you see how to use server-based techniques that include stored

procedures, views, and TVFs

■

■ Part IV: Overcoming entity errors It’s nearly impossible to create an

applica-tion that is free from error In fact, smart developers know that it is impossible

because you really never have full control over absolutely all of the code that

goes into your application This part of the book discusses three realms of error:

exceptions, concurrency issues, and performance problems

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■ Part V: Advanced management techniques This is the low-level-coding

part of the book This is where you learn how to create custom entities and use inheritance as a tool to create more robust models You also discover tech-niques for mapping various kinds of data to the Entity Framework, even when the Entity Framework normally doesn’t support the data type The key thing to remember about this part is that you discover manual methods for modifying how the automation works

Finding your best starting point in this book

The different sections of Microsoft® ADO.NET Entity Framework Step by Step cover a

wide range of technologies associated with the Entity Framework Depending on your needs and your existing understanding of Microsoft data tools, you may wish to focus

on specific areas of the book Use the following table to determine how best to proceed through the book

New to the Entity Framework Begin with Chapter 1, “Getting to know the

Entity Framework,” and move through Chapter

13, “Handling performance problems.” Skip the last part of the book until you have gained some experience using the automation that the Entity Framework provides.

Familiar with earlier releases of the Entity Framework Read through Chapter 1 and Chapter 3, “Choosing a workflow,” carefully Chapter 3 is

especially important because it helps you stand the new workflows Work through Parts III,

under-IV, and V as needed to update your knowledge Interested in learning advanced Entity Framework

techniques Move directly to Part V of the book The first four parts of this book are designed to help you learn

about the Entity Framework and interact fully with the automation it provides.

success-Interested in using the existing database structure of your organization Read Parts I and II to ensure you understand the basics of how the Entity Framework works, and

infra-then skip to Chapter 8, “Interaction with stored procedures,” Chapter 9, “Interaction with views,” and Chapter 10, “Interaction with table-valued functions.”

Every chapter in this book contains at least one hands-on example (and usually more) The only way you’ll actually gain a full understanding of the Entity Framework is

to download the sample code and then work through the hands-on examples Each of these procedures demonstrates an important element of the Entity Framework

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Conventions and features in this book

This book presents information using conventions designed to make the information

readable and easy to follow

Note Note boxed elements tell you about additional information that will prove

useful in working with the Entity Framework Notes normally include text about

techniques used to create examples or the sources of information used in creating

the chapter’s content

Tip Tip boxed elements provide additional information that will enhance your

productivity, make it easier to perform tasks, or help you locate additional sources

of information Most tips provide helpful information that you don’t need to know

in order to use the book, but the information will prove helpful later as you work

with real-world code

Warning Warning boxed elements describe potentially dangerous situations

where performing an act could result in damage to your application, the data it

manages, or the user environment (such as the need to keep certain types of

in-formation secure) Pay special attention to warning elements because they’ll save

you time and effort

■

■ Each exercise consists of a series of tasks, presented as numbered steps (1, 2,

and so on) listing each action you must take to complete the exercise

■

■ Sidebars contain useful information that isn’t part of the main flow of discussion

in a chapter These elements always have a title that tells you about the topic

of discussion You can safely skip sidebars if desired or simply read them later

Sidebars always provide you with helpful real-world resource information that

will help you as you create or manage applications

■

■ Text that you type (apart from code blocks) appears in bold

■

■ A plus sign (+) between two key names means that you must press those keys at

the same time For example, “Press Alt+Tab” means that you hold down the Alt

key while you press the Tab key

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■ A copy of Visual Studio 2012 Professional or better This book won’t work well with Visual Studio 2012 Express Edition In fact, many of the examples won’t work at all, even if you use the downloaded source code

■

■ A copy of Microsoft SQL Server 2012 Express Edition with SQL Server ment Studio 2012 Express or higher (included with Visual Studio) You can also use the full-fledged version of SQL Server 2012

Manage-Your computer must also meet these minimum requirements (although higher ings are always recommended):

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Note Many of the tasks in this book require that you have local administrator

rights Newer versions of Windows include stricter security that requires you

to have additional rights to perform tasks such as creating copies of database

files

Code samples

Most of the chapters in this book include exercises that let you interactively try out new

material learned in the main text All sample projects can be downloaded from the

fol-lowing page:

http://aka.ms/ADONETEFSbS/files

Follow the instructions to download the zip file

Note In addition to the code samples, your system should have Visual Studio

2012 Professional (or better) and SQL Server 2012 Express Edition (or better)

installed The exercises will include instructions for working with SQL Server

2012 In most cases, the exercises rely on Server Explorer to make it easy to

perform all tasks from the Visual Studio Integrated Development Environment

(IDE)

Installing the code samples

All you need to do to install the code samples is download them and unzip the archive

to a folder on your hard drive The complete source code file will include all of the

databases used in the book Simply attach these databases to your copy of SQL Server

or open them in Visual Studio by right-clicking Data Connections in Server Explorer and

choosing Add Connection Use the Microsoft SQL Server Database Connection option

when creating the connection If you encounter problems installing the code samples,

please contact me at John@JohnMuellerBooks.com You can also find answers to

com-mon questions for this book on my blog, at

http://blog.johnmuellerbooks.com/catego-ries/263/entity-framework-development-step-by-step.aspx.

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Using the code samples

The downloaded source code includes one folder for each chapter in the book Simply open the chapter folder and then the example folder for the example you want to work with in the book The downloaded source contains the completed source code so that you can see precisely how your example should look If you want to work through the examples from scratch, the book contains complete instructions for developing them.The downloaded source code also contains a Databases folder that contains all of the databases for the book Simply create a connection to the database you need to use The example will tell you which database is required If you desire, the exercises also tell you how to create the databases from scratch so that you can use whatever setup you like

Acknowledgments

Thanks to my wife, Rebecca, for working with me to get this book completed I really don’t know what I would have done without her help in researching and compiling some of the information that appears in this book She also did a fine job of proofread-ing my rough draft Rebecca keeps the house running while I’m buried in work

Russ Mullen deserves thanks for his technical edit of this book He greatly added to the accuracy and depth of the material you see here Russ is always providing me with great URLs for new products and ideas However, it’s the testing Russ does that helps most He’s the sanity check for my work Russ also has different computer equipment from mine, so he’s able to point out flaws that I might not otherwise notice

Matt Wagner, my agent, deserves credit for helping me get the contract in the first place and taking care of all the details that most authors don’t really consider I always appreciate his assistance It’s good to know that someone wants to help

A number of people read all or part of this book to help me refine the approach, test the coding examples, and generally provide input that all readers wish they could have These unpaid volunteers helped in ways too numerous to mention here I especially ap-preciate the efforts of Eva Beattie and Glenn Russell, who provided general input, read the entire book, and selflessly devoted themselves to this project

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Finally, I would like to thank my editor, Russell Jones; Christopher Hearse; Damon

Larson; and the rest of the editorial and production staff at O’Reilly for their assistance

in bringing this book to print It’s always nice to work with such a great group of

profes-sionals

Errata & book support

We’ve made every effort to ensure the accuracy of this book and its companion

con-tent Any errors that have been reported since this book was published are listed on our

Microsoft Press site at oreilly.com:

We want to hear from you

At Microsoft Press, your satisfaction is our top priority, and your feedback our most

valuable asset Please tell us what you think of this book at

http://www.microsoft.com/learning/booksurvey

The survey is short, and we read every one of your comments and ideas Thanks in

advance for your input!

Stay in touch

Let’s keep the conversation going! We’re on Twitter: http://twitter.com/MicrosoftPress.

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PART I

Introducing the Entity

Framework

Creating a database can be difficult A database models information in the real world using a

col-lection of tables, indexes, views, and other items In other words, a database is an abstraction of the

real-world information that it’s supposed to represent When a developer is tasked with creating an

application that relies on the data within a database, the developer must create a second level of

abstraction because the application won’t see the data in precisely the same way that the database

does Defining this second level of abstraction is even harder than creating the original database,

because it requires interpreting the real world through an abstraction In order to define a realistic

presentation of the data in the database—one that precisely represents the real world—a developer

needs help That’s what the Entity Framework does It provides help to a developer in the form of a

modeling methodology that eases the amount of work the developer must perform to create a

real-istic presentation To make things even easier, the Entity Framework relies on a graphical presentation

of the data so that the developer can literally see the relationships between the various tables and

other database items

Even though the concept of the Entity Framework is straightforward, you need to know more

about it before you can simply use it to create a connection between the database and your

applica-tion Working with models is definitely easier than working with hand-coded connections However,

you still need to have a good understanding of how those models work and the various ways you

can interact with them The purpose of the three chapters in this part is to introduce you to the Entity

Framework concepts You’ll use this information to build a picture of how the Entity Framework

per-forms its task so that you can perform more complex operations with the Entity Framework later in

the book

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■ Create a simple Entity Framework example.

When an architect wants to design a real-world building by creating a blueprint, one of the tools

used to ensure the blueprint is accurate is a model Often you see a model of the building as

part of the presentation for that building Models are helpful because they help others visualize the

ideas that reside in the architect’s head In addition, the models help the architect decide whether the

plan is realistic Likewise, software developers can rely on models as a means of understanding a

soft-ware design, determining whether that design is realistic, and conveying that design to others The

Entity Framework provides the means to create various kinds of models that a developer can interact

with in a number of ways As with the architect’s model, the Entity Framework uses a graphical

inter-face to make information about the underlying database structure easier to understand and modify

The Entity Framework is actually a Microsoft ActiveX Data Object NET (ADO.NET) technology

extension When you create the model of the database, you also make it possible for the Integrated

Development Environment (IDE) to automatically create some of the code required to make the

con-nection between an application and the database real Because of the way ADO.NET and the Entity

Framework interact, it’s possible to create extremely complex designs and then use those designs

directly from your code in a way that the developer will understand There isn’t any need to translate

between the levels of abstraction—the Entity Framework performs that task for you

Before you can begin using the Entity Framework to perform useful work, however, you need to

know a little more about it For one thing, you need to know why it’s called an Entity Framework It’s

also important to know how the various models work and how they’re stored on your system, should

you ever need to access them directly The following sections provide this information and more

about the Entity Framework You’ll then use the knowledge you’ve gained to create a very simple

ex-ample This example will help you better understand what the Entity Framework can do because you’ll

actually use it to interact with a simple database

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Defining an entity

An entity is the data associated with a particular object when considered from the perspective of

a particular application For example, a customer object will include a customer’s name, address, telephone number, company name, and so on The actual customer object may have more data than this associated with it, but from the perspective of this particular application, the customer object is complete by knowing these facts If you want to understand this from the traditional perspective of

a database administrator, the entity would be a single row in a view that contains all of the related information for the customer It includes everything that the database physically stores in separate tables about that particular client When thinking about entities, you need to consider these views of the data:

■

■ Physical The tables, keys, indexes, views, and other constructions that hold and describe the

data associated with a real-world object such as a customer All of these elements are mized to make it easier for the Database Management System (DBMS) to store and manipu-late the data efficiently and reliably, without error As such, a single customer data entry can appear in multiple tables and require the use of multiple keys to create a cohesive view of that customer The physical storage of the data is efficient for the DBMS, but difficult for the developer to understand

opti-■

■ Logical The combined elements required to define the data used with a single object, such

as a client From a database perspective, the logical view of the data is often encapsulated in a

view The view combines the data found within tables using keys and other database elements

that describe the relationships and order required to re-create the customer successfully Even

so, the logical view of a database is still somewhat abstract and could cause problems for the developer, not to mention require a lot of code to manage successfully ADO.NET does reduce the amount of coding the developer performs through the use of built-in objects, but the developer must still understand the underlying physical construction of that data

■

■ Conceptual The real-world view of the data as it applies to the object When you view a

customer, you see attributes that define the customer and remember items that describe the customer, such as the customer’s name A conceptual view of the data presents information in this understandable manner—as objects where the focus is on the data, not on the structure

of the underlying database

When you want to think about customers as a group, you work with entities Each entity is a single customer, and the customers as a group are entities as well In order to visualize the data that com-prises a customer, the Entity Framework relies on models These models help the developer concep-tualize the entities In addition, the Entity Framework stores these models in XML format for use in automatically generating code to create objects based on the models Working with objects makes life easier for the developer

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Note You may be tempted to think of the Entity Framework as a technology that only

ap-plies to Microsoft SQL Server and other relational databases The Entity Framework is a full solution that works with any data source, even flat-file and hierarchical databases For the sake of making the discussion clear, this book will rely upon SQL Server for the examples, but you should know that using SQL Server is only a convenience, and you can use the Entity Framework for any data source your application needs to work with In addition, you can mix and match data sources as needed within a single application

In times past, developers needed to consider the physical (tables), logical (views), and conceptual (data model) perspectives of data stored in a database A developer had to know precisely which table stored a particular piece of data, how that table was related to other tables in the database, and how to relate the data in such a way as to create a complete picture of a particular entity The developer then wrote code to make the connectivity between the application and the database work The Entity Framework reduces the need to perform such tasks A developer focuses on the entity, not the underlying physical or logical structure of the database that contains the data As a result, the developer is more productive Working with entities also makes the data easier to explain to others

An entity contains properties Just as objects are described by the properties they contain, entities

contain individual properties that describe each data element A customer’s last name would be a property of a customer entity Just as classes have configurable getters and setters, so do properties

in the Entity Framework Every entity has a special property called the key property The key property

uniquely defines the entity in some way An entity can have more than one key property, but it always has at least one An entity can also group multiple properties together to create a complex type that mimics the use of user-defined types with standard classes

Note It’s important to remember that properties can contain either simple or complex

data Simple data is of a type defined by the NET Framework, such as Int32 Complex data

is more akin to a user-defined type and consists of multiple base types within a like context

structure-It’s possible to create a relationship between two entities through an association For example, you might create an association between a customer entity and the order entities associated with the cus-tomer The association type defines the specifics of the association In some respects, an association

is similar to a database-level join One or more properties in each entity, called association endpoints,

define the relationship between the two entities The properties can define both single and umn connections between the two entities The multiplicity of the association endpoints determines whether the association is one-to-one, one-to-many, or some other combination The association

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multicol-is bidirectional, so entities have full access to each other In addition, an entity association can exmulticol-ist even when the target data lacks any form of database-level join specification All of the association

instances used to define an association type make up what is called the association set.

In order to allow one entity to view the data provided by an associated entity, the entities have a navigation property For example, a customer entity that’s associated with multiple order entities will have a navigation property that allows each order to know that it’s associated with that customer Likewise, each order will have a navigation property that allows each customer entity to see all of the orders associated with it The use of navigation properties allows your code to create a view of the en-tities from the perspective of a particular entity When working with a customer entity, the application can gain access to all of the orders submitted by that customer In some respects, this feature works much like a foreign key does in a database, but it’s easier to work with and faster to implement.Some entities derive from other entities For example, a customer can create an order However, the order will eventually have a state that creates other entities, such as a past-due order entity or a delivered-order entity These derived entities exist in the same container as the order entity as part of

an entity set You can view the relationship between entities and derived entities as being similar to

a database and its views The database contains all of the data, but a view looks at the data in a ticular way In the same way, a derived entity would help you create applications that view a particular entity type within the set of entities

par-The final piece of information you need to know for now about entities concerns the entity tainer In order to provide a convenient means to hold all of the entity information together, the Entity

con-Framework employs the entity container Before you can interact with an entity, your application

cre-ates an entity container instance This instance is known as the context Your application accesses the

entities within a particular context

Understanding the Entity Framework elements

The Entity Framework relies on XML files to perform its work These files perform three tasks: ing the conceptual model, defining the storage model, and creating mappings between the models and the physical database Even though the Entity Framework does a lot of the work for you, it’s still important to understand how these elements work together to create a better environment in which

defin-to write applications

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Note This chapter discusses the idea of models generically However, it’s important to

real-ize that the Entity Framework lets you interact with the database using one of three niques:

tech-■

■ Database first The Entity Framework creates classes that reflect an existing database

design

■

■ Design first You define a model of the database that the Entity Framework then creates

on the database server

■

■ Code first You create an application, and the Entity Framework defines a model that it

then uses to create the database on the database server

In all three cases, the Entity Framework eventually creates a model that follows the dards described in this chapter You’ll learn more about the methods of working with the Entity Framework in Chapter 3, “Choosing a workflow.” For now, the important consider-ation is the model itself

stan-Now that you a have a little idea of what constitutes the Entity Framework elements, it’s time

to discuss them in greater detail In this case, we’re looking at the logical structure of the Entity Framework The physical structure (the XML files and their content) is discussed in the “Introduc-ing the Entity Framework files” section of the chapter The following sections discuss the conceptual model, storage model, and model mappings

Considering the conceptual model

The conceptual model is the part of the Entity Framework that developers interact with most This model defines how the database looks from the application’s perspective Of course, the application view must somehow match the physical realities of the underlying database, but there are many ways

in which this happens For example, a C# application will use an INT32 value, rather than the tured Query Language (SQL) int type The conceptual model will refer to the data type as INT32, but the reality is that the database itself stores the data as an int.

Struc-The conceptual model is also used to create the classes used to interact with the database Struc-The Entity Framework manages the conceptual model As you make changes to the conceptual model, the changes are reflected in both the classes that the Entity Framework creates for your application and in the structure of the database In addition, the Entity Framework automatically tracks changes to the database design and incorporates them into your implementation classes As a result, your application can always access the data and functionality included with the target database

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Note It’s important to realize that changes to the database design can occur at several

levels The two most common levels are from the developer, when making changes to

the database model to accommodate application requirements; and from the Database Administrator (DBA), to accommodate enterprise-wide changes to the database as needed

to efficiently and reliably store information No matter how a change occurs, the database structure is ultimately affected, at which point the Entity Framework detects the change and updates the application using the data

A conceptual model also incorporates the concept of a namespace, just as your applications do An Entity Framework namespace performs the same functions as the namespace in your application For example, it helps define entities with the same name as unique features Using namespaces also helps group like entities together For example, everything related to a customer can appear in the same namespace, making it easier to interact with the customer in every way needed

At the heart of the conceptual model are the entity and association definitions used to create the view of the database Each entity definition includes the information described in the “Defining an entity” section earlier in this chapter When you use the designer to interact with the database model, what you’re really doing is modifying the XML entries that create and define each of these entity definitions The XML entries are stored on disk and used to re-create the graphic appearance of the model when you reopen the project

Considering the storage model

The storage model is the part of the Entity Framework that defines how the database looks from the database manager’s perspective However, this model provides this view within Microsoft Visual Studio, and it provides support for the conceptual model This model is often called the logical model because it provides a logical view of the database that ultimately translates into the physical database (see the “Defining an entity” section earlier in this chapter for a description of the various database views)

As with the conceptual model, the storage model consists of entity and association definitions However, these definitions reflect the logical appearance of the actual database, rather than the presentation of the conceptual model within the application In addition to the entity and association definitions, the storage model includes actual database data such as commands used to query the information within the database You’ll also find stored procedures in this model All of this additional information is used by ADO.NET to create connection and command objects automatically, so that you don’t have to hand-code the information as part of your application

Considering the model mappings

At this point, you know that there are two models used with the Entity Framework—the conceptual model presents the application view of the database and the storage model presents the logical database manager view of the database These two models are necessarily different If they were the

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same, you wouldn’t need two models The need for two models is also easy to understand once you consider that the application’s use of the database is always going to differ from the database manag-er’s goals of storing the data efficiency and reliably In order to make the two models work together, the Entity Framework requires model mapping—a third element that describes how something in the conceptual model translates to the storage model, and vice versa.

The overall goal of the model-mapping part of the Entity Framework is to create a definition of how the entities, properties, and associations in the conceptual model translate to elements within the storage model This mapping makes it possible for the application to create a connection to the database, modify its structure, manage data, and perform other tasks with a minimum of manually written code Most of the code used to interact with the database is automatically generated for the developer using the combination of the conceptual model, storage model, and this mapping layer

Introducing the Entity Framework files

As previously mentioned, all of the files used with the Entity Framework rely on XML The use of XML makes the files portable and easy to use with other applications You can also view the content of these files and reasonably expect to understand much of what they contain However, each of the Entity Framework elements uses a different XML file with a different file extension and a different language inside

After you create a new application that relies on the Entity Framework and define the required database models, you can find the resulting files in the main folder of the project When working with Visual Studio 2012, you’ll find a single Entity Data Model XML (.EDMX) file However, when working with older versions of Visual Studio, you may find individual files for each of the Entity Framework elements

Providing a complete tutorial on each of these files is outside the scope of this book The following sections provide a useful overview of the files, which you can use for further study

Viewing the Conceptual Schema Definition Language file

The Conceptual Schema Definition Language (.CSDL) file contains the XML required to build the ceptual model of the database content as viewed by the application You see this content in graphi-cal format when working with Visual Studio To see it in plain-text form, locate the CSDL or EDMX file for your application in the project folder Right-click this file in Microsoft Windows Explorer and choose Open With from the context menu Locate Notepad or some other suitable text editor in the Open With dialog box, clear any option that says that this program will become the default program for opening this file, and click OK You’ll see the XML for the conceptual model for the application

con-Following is the XML for the sample application that appears later in the chapter (some <Schema>

attributes are removed to make the listing easier to read)

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Note When using Visual Studio design tools to create the CSDL, Store Schema Definition

Language (.SSDL), and Mapping Specification Language (.MSL) files, all three are stored in

a single EDMX file, rather than in separate files Whether the data appears in a single file or within multiple files, it’s always stored as XML An EDMX file also contains some designer information not found in the separate files You can safely ignore the designer information when viewing the EDMX file in order to understand how the conceptual model, storage model, and model mapping interact

<! CSDL content >

<edmx:ConceptualModels>

</EntityType>

</Schema>

</edmx:ConceptualModels>

The XML makes it easier to understand the preceding discussion of how an Entity object works

Notice that the XML describes an entity container, used to hold all of the entities for this particular

model Within that container is a single EntityType named Customer As with all Entity objects, this one has a Key property named CustomerID that gives the Entity a unique value In addition, there are

a number of properties associated with this Entity, such as FirstName You’ll see how the properties work later in the chapter Of course, an Entity can have other elements associated with it, and you’ll

see them at work later in the book

Look at the individual <Property> entries Each one includes a NET type In this case, the types are limited to Int32 and String, but you have access to a number of other types You can see the primitive data types supported by the Entity Framework at http://msdn.microsoft.com/library/ee382832.aspx.

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Viewing the Store Schema Definition Language file

The SSDL file contains the XML required to define the storage model of the database content as viewed by the database manager As with the conceptual model, you see the database described in terms of the entities required to create it The entries rely on SQL data types, rather than NET data types Here’s an example of the XML used to create a storage model for the example that appears

later in the chapter (the <Schema> has been shortened to make the text easier to read):

</EntityType>

Viewing the Mapping Specification Language file

The MSL file creates a relationship between the CSDL and SSDL files The mapping serves to define how the application view and the database manager view reflect the same database, but from differ-ing perspectives For example, the model mapping defines which conceptual model property trans-lates into a particular storage model property Here’s the model-mapping content for the example that appears later in the chapter:

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Developing a simple Entity Framework example

The best way to begin learning about the Entity Framework is to use it This example won’t do thing too spectacular In fact, it’s downright mundane, but it does reflect a process that many devel-opers use to experiment with the Entity Framework In this case, you’ll use the model-first technique

any-to create an example application Remember that in the model-first approach, you begin by creating

a model that’s then added to the database, rather than relying on an existing database to define the model The model-first technique has the advantage of allowing you to create and manipulate a data-base that won’t have any impact on anyone else, so you’re free to experiment as much as you want.The example will start with a Windows Forms application You’ll create the model needed to make the database work with SQL Server Express (installed automatically on your system), and then use the resulting model to create a functional application You’ll test the application by managing some data you create with it The entire process will take an amazingly short time to complete, as described in the following sections

Starting the Entity Data Model Wizard

The first step is to create the database model You can perform this task using a number of methods, most of which developers never use The easy method is to start the Entity Data Model Wizard and have it do the work for you That’s the approach this example takes, as described in the following steps (you can find this project in the \Microsoft Press\Entity Framework Development Step by Step\Chapter 01\SimpleEF folder of the downloadable source code):

Tiêu đề	Microsoft ADO.NET Entity Framework Step by Step
Tác giả	John Paul Mueller
Trường học	Microsoft Corporation
Chuyên ngành	Computer Science / Software Development
Thể loại	Sách hướng dẫn
Năm xuất bản	2013
Thành phố	Sebastopol

Định dạng
Số trang	448
Dung lượng	35,54 MB